Science Fiction Writing Prompt: The Alien Shapeshifter

One recurring trope from mythology, horror, conspiracy, and science fiction is the shapeshifter.  The shapeshifter is a being that can change its physical form to mimic the form of anyone else or any other creature it sees.  There are endless varieties of shapeshifters in a variety of science fiction universes including Star Trek.  In the tinhat world of conspiracy theory, some have posited a reptilian race that can take human form and has infiltrated Earth politics and government.  

For this writing exercise, you need to come up with --

an alien being that can shapeshift and demonstrate that shapeshifting ability in a short story.

Painting by Daga Wennerström / CC BY-SA (https://creativecommons.org/licenses/by-sa/3.0)